Cementitious composition and apparatus and method for manufacturing the same

ABSTRACT

A cementitious composition capable of forming high early strength cement when admixed with water may comprise, for each 100% by weight, no more than about 60% by weight C 3 S, at least about 4% by weight C 2 S, and between about 7% and about 11% by weight SO 3 , wherein the cementitious composition has a particle size distribution such that substantially all of its particles are of a size of about 10 microns or smaller. A cementitious composition may have a ratio of weight % SO 3  to weight % Al 2 O 3  of at least about 1.5 and a particle size distribution such that substantially all of its particles are of a size of about 10 microns or smaller. An apparatus and method for making such a cementitious composition are also described.

FIELD

This application relates generally to cementitious compositions and apparatuses and methods for manufacturing the same.

BACKGROUND

Microfine cementitious compositions are generally similar to standard types of portland cement, except that such compositions have finer particle size distributions. These finer particle sizes, together with differences in chemistry, result in early setting, high strength cements. High early strength cement is desirable in numerous applications. For example, a microfine cementitious compound may be used to grout defects of oil and gas wells, that is, to fill the microscopic cracks, voids, and fissures which may be present in the formation or annular cement. Such microscopic defects are generally on the order of about 50 microns in size. Those defects are repaired when the microfine cement sets within the defects, resulting in the repair of the defects. Similarly, a microfine cementitious compound may be used to grout microscopic defects within bridges, dams, roads, airport runways, or other infrastructure projects.

Numerous physical properties determine the efficacy of microfine cementitious compositions in remediating microscopic defects. For example, a cement slurry formed from a microfine cementitious composition should be pumpable into the particular structure being remediated. Pumpability may be evaluated by reference to both the setting time and the viscosity of the cement slurry. If the slurry is too viscous, or sets too quickly, it will not be sufficiently pumpable. On the other hand, if the slurry is too viscous or sets too slowly, it may not set within the microscopic defects. The slurry should exhibit sufficiently high compressive strength to effectively reinforce the microscopic defects.

Microfine cementitious compositions make up a negligible portion of total cement produced when compared to the volume of overall portland cement production. There are five basic types of portland cement outlined by American Society for Testing and Materials (ASTM) Specification C150 and American Association of State Highway and Transportation Officials (AASHTO) Specification M 85. These standards specify such physical properties as chemical composition, fineness, soundness, consistency, setting time, compressive strength, heat of hydration, specific gravity, and loss on ignition (L.O.I.). Each one of these properties has an influence on the performance of the cement, and the different types of portland cement are therefore suited to particular applications.

For example, Type I cement is a general purpose cement used in the majority of construction, such that approximately 90% of all cement produced falls within this category. Type II cement may generally be used when a moderate sulfate resistance is desired. Type III cement may generally be used when a relatively high early strength is desired. Type III cement is similar in composition to Type I cement, except that it is much finer, with a typical Blaine fineness of about 5500 cm²/g compared to a typical fineness of about 3500 cm²/g for Type I cement. Type IV cement may generally be used when a low heat of hydration is desired, while Type V cement may generally be used where high sulfate resistance is desired. The typical chemical composition of these cement types, in % by weight, is approximately as follows:

Type Type I Type II III Type IV Type V C₃S  55%  51%  57%  28%  38% C₂S  19%  24%  19%  49%  43% C₃A  10%   6%  10%   4%   4% C₄AF   7%  11%   7%  12%   9% SO₃ 2.9% 2.5% 3.1% 1.9% 1.8% MgO 2.8% 2.9% 3.0% 1.8% 1.9% L.O.I. 1.0% 0.8% 0.9% 0.8% 0.9%

The setting of cement involves the chemical reaction of hydration. In general terms, the early hydration of cement is principally controlled by the amount and activity of C₃A, balanced by the amount and type of SO₃ interground with the cement. As the fineness of C₃A within a cement increases, the activity of the Al₂O₃ rises due to an increase in reactive surface area. Consequently, the greater the fineness of C₃A within a cement, the higher the concentration of SO₃ required to inhibit the Al₂O₃. C₃A hydrates very rapidly and will influence early bonding characteristics. If this hydration is not properly controlled by the sulfate, problems such as flash set, false set, slump loss, and cement-admixture incompatibility may result.

Of particular concern is the problem of false set, also known as early stiffening or premature stiffening, which may occur when an excessive amount of hemihydrate, i.e., the partially dehydrated form of gypsum (CaSO₄.½H₂O), is present in the cement. In particular, false set is primarily caused by the rehydration of hemihydrate back to gypsum, which precipitates out of the cement slurry. This gypsum precipitate causes the appearance of setting, when in reality the hydration of C₃A has not yet begun in earnest, and is further inhibited by the presence of gypsum.

SUMMARY

A cementitious composition capable of forming high early strength cement when admixed with a liquid may comprise, for each 100% by weight, no more than about 60% by weight C₃S, at least about 4% by weight C₂S, and between about 7% and about 11% by weight SO₃, wherein the cementitious composition has a particle size distribution such that substantially all of its particles are of a size of about 10 microns or smaller. A cementitious composition may have a ratio of weight % SO₃ to weight % Al₂O₃ of at least about 1.7 and a particle size distribution such that substantially all of its particles are of a size of about 10 microns or smaller. An apparatus and method for making such a cementitious composition are also described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an apparatus and process for manufacturing a microfine cementitious composition.

DETAILED DESCRIPTION

As used herein, the following terms should be understood to have the indicated meanings:

When an item is introduced by “a” or “an,” it should be understood to mean one or more of that item.

“Classifier” means a device for separating solids of different characteristics by controlled rates of settling.

“Comprises” means includes but is not limited to.

“Comprising” means including but not limited to.

“Having” means including but not limited to.

“Cementitious” means of or relating to a chemical substance having the characteristics of cement.

“Clinker” means a material comprising hydraulic calcium silicates. Clinker may be sintered into lumps or nodules, typically of a diameter no greater than about 3 inches, or other suitable size.

“Feed” means a device adapted for feeding one or more materials.

“Grinding” means to reduce or lessen into relatively smaller particles or pieces by pulverizing, pounding, cutting, crushing, grating, rubbing harshly, carving, sawing, trimming, or dissolving, or a combination thereof.

“Hemihydrate” means partially dehydrated gypsum, also commonly referred to as plaster of paris, which has a chemical formula of CaSO₄.½H₂O.

“Hydraulic” means able to set and harden by reacting with water, while also forming a water-resistant product.

“Inhibit” means to at least partially decrease the activity of an active chemical reagent, such as, for example, Al₂O₃.

“Microfine” means of or pertaining to units of measure described in terms of microns.

“Portland cement” is a type of hydraulic cement produced by pulverizing clinker with one or more forms of calcium sulfate, usually in the form of gypsum. Numerous processing additions, in addition to clinker and gypsum, may also be present.

“Remainder portion” means the portion of a bulk material that is not scalped.

“Scalping” means to remove a portion of a bulk material, whether such bulk material is in a continuous process stream or stored in a batch storage system or otherwise.

“Setting” and “set” mean the solidification and hardening of a cement slurry.

“Silo” means any object, space, or area suitable for storing a cementitious compound, such as, for example, holding tanks, rail cars, pits, or drop piles.

“Grouting” means the filling of a microscopic void with a microfine cementitious composition.

“Slurry” means a suspension of a solid in a liquid.

“Standardized portland cement” means a hydraulic cement having physical characteristics which satisfy a standardized cement type, such as, for example, the cement types described by the American Society for Testing and Materials in ASTM Specification C150 or those described by the American Association of State Highway and Transportation Officials in AASHTO Specification M 85.

The present application is directed to a microfine cementitious composition capable of forming a high, early-strength cement when admixed with a liquid. The application is also directed to an apparatus and method for making a microfine cementitious composition, which involves the scalping of microfine particles from a standardized portland cement.

In one embodiment, a microfine cementitious composition may be formed having a particle size distribution such that substantially all of its particles are of a size of about 10 microns or smaller, resulting in a surface area, i.e., Blaine fineness, of at least about 1,000 m²/kg. The chemical composition of one embodiment of such cementitious composition may comprise for each 100% by weight, no more than about 60% by weight C₃S, at least about 4% by weight C₂S, and between about 7% and about 11% by weight SO₃. Such embodiment of microfine cementitious composition may also have a ratio of weight % SO₃ to weight % Al₂O₃ of at least about 1.5.

The resultant microfine cementitious composition may be admixed with water or another suitable liquid to form a cement slurry. Such composition may also be admixed with sand and/or aggregates as is conventional with cement slurry preparation. For example, in one embodiment, a cement slurry may be formed by adding water at about 140% to about 150% by weight of the microfine cementitious composition. A person having ordinary skill in the art will understand that other processing additions may also be incorporated to the cement slurry, including, for example, microfine sand, accelerators, retarders, loss-circulation control agents, deairing control agents, and friction reducers. Suitable amounts of other additives may also be used such that they do not adversely affect the pumpability of the cement slurry or strength of the cement which results from setting of the cement slurry.

The cement slurry may have an initial consistency of greater than about 10 Bearden units of consistency (B_(c)), which is a dimensionless quantity used to measure the pumpability of a substance as known by persons of ordinary skill in the art. The thickening time of the cement slurry, or the time required for the cement slurry to reach what is generally considered the maximum pumpable consistency of 70 B_(c), generally may be greater than about 90 minutes. The viscosity of the cement slurry, measured at 80° F. using a Model 35A Fann Viscometer and a No. 1 spring, may be greater than about 90 cps at 300 RPM. The compressive strength of the cement slurry may be between about 200 psi and about 500 psi after 24 hours, and between about 500 psi and about 700 psi after 7 days. The testing conditions under which the preceding properties of consistency, thickening time, viscosity, and compressive strength were measured are described in greater detail below in the cited examples. Of course, other suitable values for those properties may also be employed.

A microfine cementitious composition as described herein may be utilized in any environment where high early strength is desired. For example, in one embodiment, a slurry of a microfine cementitious composition may be used for cementing operations in oil and gas wells, more particularly, in grouting the cement casings of oil and gas wells. In such an application, the slurry may be pumped into the annulus between the bore hole and the formation, or into the formation directly, such that the microfine cement is forced into the small cracks, voids, and fissures which may be present in the casing; such defects generally being on the order of about 50 microns in size. The microfine cement then sets within the pore defects, resulting in the repair and remediation of the defects. A person having ordinary skill in the art will understand that numerous other remedial uses exist for a microfine cementitious composition as described herein. For example, a slurry of a microfine cementitious composition may be injected into the void spaces of bridges, dams, roads, airport runways, or other infrastructure projects in order to fill microscopic defects within such structures.

The present application is also directed to a method and apparatus for making such a microfine cementitious compound. One embodiment of the method by which a microfine cementitious composition may be made is illustrated by reference to the apparatus of FIG. 1. Referring to FIG. 1, clinker and gypsum in the feed bins 10 and 12, respectively, are passed in the desired proportions in flow line 14 to a grinding mill 16. The output of the grinding mill 16 is then passed by flow line 18 into a first classifier 20, for example an air separator commonly used in the manufacture of cement, which separates out the coarser particles from finer particles which constitute a standard portland cement. ASTM Specification C150 and AASHTO Specification M 85 define the physical properties of some standardized forms of portland cement, and a person having ordinary skill in the art will understand that various proportions of clinker and gypsum may be used to create such standardized portland cements. Furthermore, numerous other materials 13 may be added to the clinker and gypsum feed stream in flow line 14 to create standardized or specialized forms of portland cement. For example, coal combustion products, such as fly ash; residual products from industrial smelting processes, such as blast furnace slag; and limestone may all be added to the clinker and gypsum, either alone or in combination.

Still referring to FIG. 1, the coarser output of the first classifier 20 may be returned by means of a flow line 22 to the input flow line 14 to the grinding mill 16 for further grinding. The finer output from the classifier 20 may then be transferred to a cooler 26 by means of a flow line 24 to cool the finer output and prevent formation of hemihydrate. The rate of formation of hemihydrate in the cement of flow line 24 depends on a number of factors, such as the bulk temperature of the cement within the grinding mill 16, the residence time of the cement at the bulk temperature, the relative humidity of the air, and the ambient temperature. A person having ordinary skill in the art will understand that cooler 26 may be operated in various ways so as to inhibit the formation of hemihydrate. For example, in a typical Type I cement grinding process having a bulk temperature of about 260° F., which produces about 1500 tons of cement every 24 hours at a relative humidity of about 80% and ambient temperature of about 80° F., the formation of hemihydrate may be inhibited by operating cooler 26 such that the bulk temperature of the cooled cement output from cooler 26 in flow line 28 is kept below about 135° F. If desired, output of the cooler 26 may then be transferred to storage silo 30 by means of a flow line 28 to provide a standard portland cement.

To obtain a cementitious composition having substantially all of its particles of about 10 microns and smaller, a portion of the output of the cooler 26 may be diverted from flow line 28 to a second classifier 32 by means of a flow line 34. A person having ordinary skill in the art will understand that numerous devices may be used to divert a portion of the output of the cooler 26 to control the rate of feed to the second classifier 32, such as, for example, using a flapper valve and feeder, or using a diverter partition with a metering device. In one embodiment, the portion of the output of the cooler 26 diverted to the second classifier 32 may be greater than about 10% by volume and less than about 30% by volume of the output of the cooler 26, though a person having ordinary skill in the art will recognize that a smaller or larger portion of the output of the cooler 26 may be used depending on the desired rate of manufacture of the microfine cementitious composition. The process of diverting a portion of a flow line is known as scalping.

A person having ordinary skill in the art will further recognize that cooler 26 may be situated on any number of process flow lines in order to cool the cementitious composition. For example, cooler 26 may also be positioned on flow line 18 to cool the output from the grinding mill 16, flow line 22 to cool the coarser output of the first classifier 20, flow line 28 to cool the finer output of the first classifier 20 and coarser output of the second classifier 32, and/or on flow line 38 to cool the finer output from the second classifier 32. Any number of coolers may be used at any desired location and in any combination.

The second classifier 32 may be a centrifugal, fine particle classifier that disburses and then classifies the particles into a coarser output of greater than about 10 microns and a finer output of about 10 microns and smaller. For example, a Classiclon™ CC-F ultrafine classifier sold by PM-Technologies, GmbH or an MS-20 classifier sold by RSG, Inc. may be used, or any other suitable classifier. The coarser output of the second classifier 32 (sometimes referred to herein as a secondary portion) may be returned to flow line 28 by means of flow line 36 such that said coarser output is transferred to storage silo 30. Alternatively, said coarser output from second classifier 32 may be transferred directly to storage silo 30.

The finer output of the second classifier 32, i.e., the particles of about 10 micron size and smaller, which is sometimes referred to herein as a primary portion, may be transferred by flow line 38 to storage silo 40. In one embodiment, the coarser particles rejected by the second classifier 32 may be returned to flow line 28 or transferred directly to storage silo 30 such that both the composition of the finer output of the first classifier 20 and the cementitious composition in storage silo 30 exhibit physical characteristics indicative of the same type of standardized portland cement, such as, for example, Type I portland cement. In such an embodiment, the scalping of some of the particles of about 10 micron size and smaller from a standardized portland cement in flow line 28 may occur without changing the classification of such standardized portland cement, e.g., the scalping of Type I portland cement may result in both a microfine cementitious composition and a Type I portland cement. Alternatively, the scalping of a Type I portland cement may result in both a microfine cementitious composition and another type of specialty cement. Other types of cement products may also be produced if desired.

In another embodiment, the elements indicated by the dotted line of region A, i.e., the second classifier 32, flow lines 34, 36, and 38, and storage silo 40, may be used in conjunction with a standardized portland cement, whether such standardized cement is in a continuous process stream, as indicated by flow line 28 of FIG. 1, or stored in a batch storage system. For example, the elements indicated by the dotted line of region A may be retrofitted into preexisting portland cement production facilities, or may be operated separately from such facilities, so as to create a microfine cementitious composition in addition to the preexisting portland cement. As a result, only minimal changes to the current manufacturing process for standard portland cements may be made.

In one embodiment, the material in flow line 28 may be a Type III portland cement and the resulting microfine cementitious composition may have, for each 100% by weight, between about 3% and about 7% by weight SO₃. In another embodiment, the material in flow line 28 may be a Type I portland cement and the resulting microfine cementitious composition may have, for each 100% by weight, between about 7% and about 11% by weight SO₃. The higher SO₃ concentration in a microfine cementitious composition made from Type I portland cement is surprising and counterintuitive, since Type I cement generally has a lower concentration of SO₃ than Type III cement, namely, between about 2.9% and about 3.5% by weight SO₃ in Type I cement compared to between about 3.1% and about 4.5% by weight SO₃ in Type III cement. Type I portland cement is the most prevalent form of portland cement, constituting approximately 90% of all portland cement production. Type I cement is also generally the least expensive type of portland cement.

A person having ordinary skill in the art will understand that the overall concentration of SO₃ in the microfine cementitious composition may be controlled by adjusting the rotor tip velocity in the second classifier 32. For example, in one embodiment, a 12-inch diameter rotor operated at about 3000 RPM, and having a rotor tip velocity of about 160 fps, may be used to create a microfine cementitious composition comprising between about 7% and about 11% by weight SO₃. A similar composition may also be achieved, for example, by operating a 13-inch diameter rotor at about 3000 RPM, and having a rotor tip velocity of about 170 fps.

Embodiments of the invention will be further described in connection with the following examples, which are set forth for purposes of illustration only:

EXAMPLE 1

A cementitious composition was prepared from Type I portland cement. More particularly, a cementitious composition was formed by admixing about 93% by weight of clinker and about 7% by weight of gypsum, feeding such mixture into a grinding mill circuit and cooler to produce a Type I portland cement discharge stream, and then feeding about 10% by volume of said discharge stream into a high efficiency air separator operated so as to separate particles of a size of about 10 microns and less. The coarser particles rejected by the separator were returned to the discharge stream such that the overall composition of the discharge stream maintained the characteristics of a Type I portland cement.

The specific gravity of the cementitious composition was about 2.92 and the ratio of SO₃:Al₂O₃ was about 2.42. The cementitious composition was tested for compressive strength in accordance with API Spec 10A. More particularly, water was admixed with the dry cementitious composition, in values relative to the weight of the cementitious composition, namely, water at about 141% by weight of the cementitious composition. The mixture was allowed to harden at about 80° F. and atmospheric pressure, with about 100% humidity, which resulted in a compressive strength, measured after 24 hours, of about 270 psi.

To determine the pumpability of the cementitious composition, a cement slurry was prepared according to the procedures outlined in API Schedule 9.2. The initial cement slurry viscosity in Bearden units of consistency (B_(c)) was about 10 B_(c). The cement slurry was then heated to a test temperature of about 80° F. to determine the thickening time, or the time required for the cement slurry to reach what is generally considered the maximum pumpable consistency of about 70 B_(c). The cement slurry reached a consistency of about 70 B_(c) in about 0:20 hr:min. The viscosity of the cement slurry was also measured at about 80° F. using a Model 35A Fann Viscometer, which is a rotational type rheometer and a No. 1 spring. The mean particle size was about 2.3 microns. The cementitious composition had the following particle size distribution, chemistry and viscosity:

A. Particle size distribution % Under 9.00 microns 100.00% % Under 4.19 microns 81.73% % Under 1.95 microns 43.51% B. Chemistry % by Weight C₃S 52.72% C₂S 6.74% C₃A 8.75% C₄AF 4.52% CaO 57.98% SiO₂ 16.22% SO₃ 10.29% Al₂O₃ 4.25% MgO 1.03% Fe₂O₃ 1.49% K₂O 1.63% TiO₂ 0.27% Na₂O 0.23% Trace Oxides 0.66% L.O.I. 5.95% C. Viscosity RPM cps 300 174 200 152 100 125  60 110  30 92  6 56  3 43 10 Second Gel 41 10 Minute Gel 43

EXAMPLE 2

A cementitious composition was prepared as in Example 1, except that the composition had a specific gravity of about 3.09 and a ratio of SO₃:Al₂O₃ of about 1.59. The compressive strength of the composition, measured after 24 hours as in Example 1, was about 430 psi. The compressive strength measured after 7 days was about 540 psi. The initial viscosity of the cement slurry, prepared as in Example 1, was about 8 B_(c) and the slurry reached a consistency of about 70 B_(c) in about 3:21 hr:min. The viscosity of the cement slurry was measured as in Example 1. The mean particle size was about 1.7 microns. The cementitious composition had the following particle size distribution, chemistry and viscosity:

A. Particle size distribution % Under 7.72 microns 100.00% % Under 4.19 microns 91.73% % Under 1.95 microns 58.24% B. Chemistry % by Weight C₃S 56.15% C₂S 9.82% C₃A 10.57% C₄AF 5.71% CaO 58.40% SiO₂ 16.92% SO₃ 7.69% Al₂O₃ 4.83% MgO 1.20% Fe₂O₃ 1.75% K₂O 1.41% TiO₂ 0.20% Na₂O 0.20% Trace Oxides 0.50% L.O.I. 6.90% C. Viscosity RPM cps 300 183 200 162 100 133  60 120  30 100  6 59  3 59 10 Second Gel 21 10 Minute Gel 61

EXAMPLE 3

A cementitious composition was prepared as in Example 1, except that the composition had a specific gravity of about 3.09 and a ratio of SO₃:Al₂O₃ of about 1.52. The compressive strength of the composition, measured after 24 hours and after 7 days as in Example 2, was about 450 psi and about 600 psi, respectively. The initial viscosity of the cement slurry, prepared as in Example 1, was about 13 B_(c) and the slurry reached a consistency of about 70 B_(c) in about 3:52 hr:min. The viscosity of the cement slurry was measured as in Example 1. The mean particle size was about 1.7 microns. The cementitious composition had the following particle size distribution, chemistry and viscosity:

A. Particle size distribution % Under 6.63 microns 100.00% % Under 4.19 microns 91.77% % Under 1.95 microns 56.97% B. Chemistry % by Weight C₃S 58.62% C₂S 9.58% C₃A 10.73% C₄AF 5.77% CaO 57.96% SiO₂ 16.81% SO₃ 7.34% Al₂O₃ 4.84% MgO 1.20% Fe₂O₃ 1.75% K₂O 1.35% TiO₂ 0.22% Na₂O 0.23% Trace Oxides 0.12% L.O.I. 8.20% C. Viscosity RPM cps 300 165 200 146 100 117  60 103  30 84  6 45  3 37 10 Second Gel 36 10 Minute Gel 50

EXAMPLE 4

A cementitious composition was prepared as in Example 1, except that the Type I portland cement discharge stream was formed by admixing about 89% by weight of clinker, about 4.5% by weight of gypsum, about 2.5% by weight of limestone, and about 4% by weight of granulated blast furnace slag. The composition had a specific gravity of about 3.01 and a ratio of SO₃:Al₂O₃ of about 2.66. The compressive strength of the composition, measured after 24 hours and after 7 days as in Example 2, was about 470 psi and about 550 psi, respectively. The initial viscosity of the cement slurry, prepared as in Example 1, was about 4 B_(c) and the slurry reached a consistency of about 70 B_(c) in about 3:41 hr:min. The viscosity of the cement slurry was measured as in Example 1. The mean particle size was about 1.4 microns. The cementitious composition had the following particle size distribution, chemistry and viscosity:

A. Particle size distribution % Under 9.00 microns 100.00% % Under 4.19 microns 90.08% % Under 1.95 microns 62.57% B. Chemistry % by Weight C₃S 52.09% C₂S 9.45% C₃A 9.47% C₄AF 4.62% CaO 58.99% SiO₂ 16.28% SO₃ 11.55% Al₂O₃ 4.35% MgO 1.16% Fe₂O₃ 1.45% K₂O 1.38% TiO₂ 0.22% Na₂O 0.22% Trace Oxides 0.14% L.O.I. 4.26% C. Viscosity RPM cps 300 183 200 162 100 133  60 120  30 100  6 59  3 59 10 Second Gel 21 10 Minute Gel 61

EXAMPLE 5

A cementitious composition was prepared as in Example 4, except that the composition had a specific gravity of about 3.04 and a ratio of SO₃:Al₂O₃ of about 2.07. The compressive strength of the composition, measured after 24 hours and after 7 days as in Example 2, was about 410 psi and about 590 psi, respectively. The initial viscosity of the cement slurry, prepared as in Example 1, was about 9 B_(c) and the slurry reached a consistency of about 70 B_(c) in about 4:01 hr:min. The viscosity of the cement slurry was measured as in Example 1. The mean particle size was about 2.0 microns. The cementitious composition had the following particle size distribution, chemistry and viscosity:

A. Particle size distribution % Under 10.48 microns 100.00% % Under 4.19 microns 83.43% % Under 1.95 microns 52.65% B. Chemistry % by Weight C₃S 49.63% C₂S 9.87% C₃A 9.31% C₄AF 4.52% CaO 57.48% SiO₂ 16.72% SO₃ 9.01% Al₂O₃ 4.35% MgO 1.58% Fe₂O₃ 1.24% K₂O 1.31% TiO₂ 0.20% Na₂O 0.19% Trace Oxides 0.25% L.O.I. 7.68% C. Viscosity RPM cps 300 118 200 102 100 81  60 70  30 55  6 34  3 28 10 Second Gel 28 10 Minute Gel 33

EXAMPLE 6

A cementitious composition was prepared as in Example 4, except that the composition had a specific gravity of about 3.05 and a ratio of SO₃:Al₂O₃ of about 1.59. The compressive strength of the composition, measured after 24 hours and after 7 days as in Example 2, was about 350 psi and about 560 psi, respectively. The initial viscosity of the cement slurry, prepared as in Example 1, was about 4 B_(c) and the slurry reached a consistency of about 70 B_(c) in about 4:55 hr:min. The viscosity of the cement slurry was measured as in Example 1. The mean particle size was about 2.3 microns. The cementitious composition had the following particle size distribution, chemistry and viscosity:

A. Particle size distribution % Under 10.48 microns 100.00% % Under 4.19 microns 80.14% % Under 1.95 microns 47.21% B. Chemistry % by Weight C₃S 46.01% C₂S 15.50% C₃A 10.97% C₄AF 3.88% CaO 58.20% SiO₂ 17.54% SO₃ 7.87% Al₂O₃ 4.96% MgO 1.41% Fe₂O₃ 1.28% K₂O 1.15% TiO₂ 0.19% Na₂O 0.17% Trace Oxides 0.25% L.O.I. 7.01% C. Viscosity RPM cps 300 95 200 84 100 70  60 60  30 49  6 30  3 23 10 Second Gel 23 10 Minute Gel 28

EXAMPLE 7

A cementitious composition was prepared as in Example 4, except that the composition had a specific gravity of about 3.01 and a ratio of SO₃ :Al₂O₃ of about 2.16. The compressive strength of the composition, measured after 24 hours and after 7 days as in Example 2, was about 350 psi and about 520 psi, respectively. The initial viscosity of the cement slurry, prepared as in Example 1, was about 5 B_(c) and the slurry reached a consistency of about 70 B_(c) in about 3:48 hr:min. The viscosity of the cement slurry was measured as in Example 1. The mean particle size was about 2.0 microns. The cementitious composition had the following particle size distribution, chemistry and viscosity:

A. Particle size distribution % Under 9.00 microns 100.00% % Under 4.19 microns 83.86% % Under 1.95 microns 49.65% B. Chemistry % by Weight C₃S 40.51%  C₂S 17.32%  C₃A 10.36%  C₄AF  3.6% CaO 56.6% SiO₂ 16.79%  SO₃ 10.12%  Al₂O₃ 4.69% MgO 1.35% Fe₂O₃ 1.19% K₂O 1.12% TiO₂ 0.18% Na₂O 0.16% Trace Oxides 0.27% L.O.I. 7.55% C. Viscosity RPM cps 300 99 200 89 100 72  60 62  30 49  6 29  3 23 10 Second Gel 23 10 Minute Gel 32

Although the foregoing specific details describe certain embodiments of this invention, persons reasonably skilled in the art will recognize that various changes may be made in the details of this invention without departing from the spirit and scope of the invention as defined in the appended claims and considering the doctrine of equivalents. Therefore, it should be understood that this invention is not to be limited to the specific details shown and described herein. 

1. A cementitious composition comprising: no more than about 60% by weight C₃S; at least about 4% by weight C₂S; and between about 7% and about 11% by weight SO₃; wherein said cementitious composition has a particle size distribution such that substantially all of its particles are of a size of about 10 microns or smaller.
 2. The cementitious composition of claim 1 wherein said composition comprises between about 40% and about 60% by weight C₃S.
 3. The cementitious composition of claim 1 wherein said composition comprises between about 4% and about 20% by weight C₂S.
 4. The cementitious composition of claim 1 wherein said composition has a mean particle size less than about 3 microns.
 5. The cementitious composition of claim 1 wherein said composition comprises between about 40% and about 50% by weight C₃S; and between about 15% and about 20% by weight C₂S.
 6. A cementitious composition comprising: SO₃; and Al₂O₃; wherein said cementitious composition has a ratio of weight % SO₃ to weight % Al₂O₃ of at least about 1.5; and wherein said cementitious composition has a particle size distribution such that substantially all of its particles are of a size of about 10 microns or smaller.
 7. The cementitious composition of claim 6 wherein said composition has a mean particle size less than about 3 microns.
 8. A method for making a cementitious composition comprising: scalping a first stream of Type I portland cement so as to separate said first stream into a primary portion and a secondary portion, said primary portion having a particle size distribution such that substantially all of its particles are of a size of about 10 microns or smaller; and combining said secondary portion with a remainder portion of said first stream of Type I portland cement to form a resultant cementitious composition; wherein said resultant cementitious composition is selected from Type I portland cement and Type III portland cement.
 9. The method for making a cementitious composition of claim 8 wherein said primary portion has a mean particle size less than about 3 microns.
 10. A method for making a cementitious composition comprising: scalping a first stream of portland cement so as to separate said first stream into a primary portion and a secondary portion, said primary portion having a particle size distribution such that substantially all of its particles are of a size of about 10 microns or smaller; and combining said secondary portion with a remainder portion of said first stream of portland cement to form a resultant cementitious composition; wherein said resultant cementitious composition is selected from Type I portland cement and Type III portland cement.
 11. The method for making a cementitious composition of claim 10 wherein said primary portion has a mean particle size less than about 3 microns. 